Wireless Channel Characteristics Research Articles

Multipath and Doppler Characterization of an Electromagnetic Environment by Massive MDT Measurements From 3G and 4G Mobile Terminals

This paper describes an innovative approach to radio channel characterization in UMTS and LTE mobile networks. In place of traditional drive tests (DT), which employ a single test mobile, a massive collection of georeferenced radio measurements is made from a wide population of user equipment (UE). This is possible with new 3GPP features, called “minimization of DTs” (MDT), which are implemented in the last generation UEs and enable the reporting of additional periodical measurements, including GPS position and estimated UE distance (i.e. delay) over the radio path. This opens to new fields of investigation in the mobile radio channel, unreachable with the legacy DT approach, such as multipath and Doppler analysis. The UE MDT data of UMTS and LTE RAN of Telecom Italia Mobile, in the Italian midsized city of Bologna, have been statistically analyzed. The big data elaboration has been performed with the Nokia proprietary system “GeoSynthesis.” The results give a high-resolution geographical view of the above-mentioned channel phenomena affecting the quality and user experience. They are in good accordance with network performance indicators: the higher the multipath time, the worse the decoding performance of radio blocks (block error rate). The estimated Doppler shift also fits the known mobility patterns in the urban environment.

Radio Channel Characterization of Mid-Band 5G Service Delivery for Ultra-Low Altitude Aerial Base Stations

This paper presents a study which evaluated the potential for using ultra-low altitude, unmanned aerial vehicles to deliver fifth-generation (5G) cellular connectivity, particularly into areas requiring short-term enhancement in coverage. Such short-term enhancement requirements may include large gatherings of people or during disaster scenarios where there may be service outages or a need for increased bandwidth. An evaluation of this approach was conducted with empirically generated results regarding signal quality and cellular coverage—illustrating the potential of using unmanned ultra-low altitude aerial vehicles to deliver 5G cellular mobile services. Specifically, channel gain, mean time delay of the received signals ( $\tau _{\textrm {mean}}$ ), and the root-mean-square spread of the delay ( $\tau _{\textrm {rms}}$ ) were investigated for two distinct user modes at three different drone heights for three selected environments—an open area (field), a tree-lined environment, and an enclosed area. Maximum likelihood estimates for the various drone heights, user modes, and operational environments were found to be Rician distributed for the received signal strength measurements, whereas $\tau _{\textrm {mean}}$ and $\tau _{\textrm {rms}}$ for the open and tree-lined environments were Weibull distributed with the enclosed area tests being lognormally distributed. The paper also investigates how the channel gain may be affected when operating in each of the various global bands allocated for mid-5G communications, namely, Europe, China, Japan, South Korea, and North America. These regional mid-5G band allocations were found to yield minimal variance for all the environments considered.

In Underground Vehicular Radio Channel Characterization

Vehicular communication is characterized by a dynamic environment and high mobility. In this paper we present a shadow fading model targeting system simulations based on real measurements performed in underground gallery. As first results, we present in this paper the delay spread statistics for each investigated environment. We also study the large-scale, small-scale fading and extract some time channel parameters such as root-mean-square (RMS) delay for a realistic underground propagation environment at 5.9 GHz. Since there are so far few published results for these confined environments, the results obtained can be useful for the deployment of vehicular-to-vehicular (V2V) and vehicular-to-infrastructure (V2I) communication systems inside underground mines galleries.

Unified and fast handover authentication based on link signatures in 5G SDN‐based HetNet

Existing handover authentication schemes are implemented in the upper layer through cryptographic techniques with different protocols and parameters involved under different handover scenarios, introducing high latency and complexity especially in the next generation (5G) highly heterogeneous network (HetNet). The authors propose to introduce wireless link signatures decided by users' locations as handover authentication data to achieve unified and fast handover authentication at the physical layer in 5G software defined networking-based HetNet. Specifically, the unique wireless channel characteristics between a user and the serving access point (AP) are extracted as the secure context information (SCI) and transferred to the target AP. The latter determines whether the user is the legitimate one who has already been authenticated according to the received SCI. They then analyse the authentication performance relating to multiple attributes and results demonstrate that the authentication strength can be adaptively adjusted. Furthermore, they find that optimum performance can be achieved by setting a proper decision threshold and derive the sub-optimal performance by iterative search. Lastly, analysis and simulations on latency and overhead compared with existing ones are conducted and results prove the effectiveness of the proposed scheme.

Hand Palm Local Channel Characterization for Millimeter-Wave Body-Centric Applications

The body-centric wireless channel characterization mostly utilizes whole body models. However, localized channels for body parts consistently interacting with the wireless device have their own importance. This paper attempts to characterize the hand palm local channel through experimental measurements at three millimeter-wave frequency bands of 27-28 GHz, 29-30 GHz, and 31-32 GHz. Five human subjects are used in this study. Net body loss is found to be 3dB for different subjects with subject-specific and varying palm shape size is found to be the primary affecting source. The repeatability of the on-body propagation measurements is found to be within 10% of variance.

Diffraction loss model at 0.3–6 GHz for 5G cellular system in microcell urban areas

ABSTRACTThe 0.3–6 GHz band will be a key component of fifth-generation (5G) wireless cellular communication systems. This paper presents non-line of sight (NLOS) radio propagation channel characteristics and considers a fundamental issue of diffraction loss (DL) and shadowing phenomena modeling for urban cellular communication systems in this band. Moreover, the channel capacity (CP) is investigated under the influence of antenna mutual coupling (MC). In this respect, the uniform theory of diffraction (UTD) is utilized to accurately calculate multiple building diffraction loss. In this channel model, diffracted and reflected–diffracted rays are involved in the propagation mechanism based on two urban structures for single input single output (SISO) and multiple input multiple output (MIMO) systems. The paper compares measurements conducted at 2 GHz and 5 GHz radio-channel sounder system in the NLOS urban microcell of Oulu in Finland with UTD simulations made for the same areas. The comparison shows a good agreement between them.

Fast secret key generation based on dynamic private pilot from static wireless channels

In static or quasi-static wireless channel environments, secret key generation (SKG) based on wireless channels is vulnerable to active attacks due to the openness and invariance of public pilot, especially man-in-the-middle (MITM) attacks, where attacker acts as a transparent relay to manipulate channel measurements and derive the generated keys. In order to fight against this attack, a dynamic private pilot is designed, where both private pilot and secret key are derived from the characteristics of wireless channels and private to third party. In static or quasi-static environments, we use singular value decomposition techniques to reconstitute the wireless channels to improve the randomness of the wireless channels. Private pilot can encrypt and authenticate the wireless channels, which can make channel state information intercepted by MITM attacker reduced to zero and the SKG rate close to that without attacks. Results of analysis and simulation show the proposed SKG scheme can withdraw the MITM attacks.

Energy efficient resource matching algorithm for multi-homing services in dynamic wireless environment

This paper investigates the matching problem between radio resources and multi-homing services in a dynamic heterogeneous wireless environment. A mobile terminal with a multi-homing service simultaneously transmits data to multiple radio access networks using multiple air interfaces. This paper proposes an energy-efficient resource matching algorithm to statistically guarantee the service rate requirements of each user with the lowest power consumption. First, according to the concept of resource matching and the dynamic characteristics of wireless channels, this paper defines two matching probability metrics and subsequently selects the most appropriate metric to build a resource matching model to realize the maximum energy efficiency of each user while meeting the statistical guarantee constraints. In particular, the Rayleigh fading channel model is introduced in this paper to accurately reflect the dynamics of the wireless channel, and a complete expression of the matching probability metric is deduced. Second, according to the optimal solution characteristics of the optimization model, the original problem is decomposed into the inner power minimization problem and the outer matching probability maximization problem, and the convex optimization and the equality constrained optimization are separately used to solve the problem. Hence, the two-layer distributed solution algorithm is proposed. In particular, this paper conducts rigorous mathematical analyses on the convergence, optimality and complexity of the algorithm and constructs an improved resource matching model by relaxing the statistical guarantee parameters in the case of no solution to the model. Finally, the simulation results show that this algorithm has better performance than the three existing resource matching algorithms, can achieve lower user power consumption, and can realize the goal of the best match between the network resources and service requirements in a dynamic environment.

Improving Multipath TCP Performance over WiFi and Cellular Networks: An Analytical Approach

A complete understanding of the dynamics of Multipath TCP (MPTCP) over Cellular and WiFi networks is still lacking. This is a highly challenging issue, as a consequence of the complex interdependencies between the losses, packet reordering due to heterogeneous wireless channel features, errors, and link layer retransmissions, as well as their (joint) influence on MPTCP's control mechanism. In this paper, we develop a comprehensive approach that is capable of assessing the performance of long-lived MPTCP flows with joint WiFi and Cellular network access, taking into account the diverse characteristics of both types of networks. Relying on a parallel queueing model, we develop a framework that features the controllable network parameters, such as the retransmission limit and the buffer sizes, so as to capture their impact on the TCP-level performance. We include a variety of numerical and simulation results highlighting various non-trivial findings and insights for adaptive MPTCP design. In particular, we design a novel MPTCP algorithm to exploit the route heterogeneity, and demonstrate that the proposed algorithm is capable of learning the network's characteristics. It also identifies the improved MPTCP window increment parameters for any given set of channel errors, retransmission limits, and buffer sizes.

V2V radio channel properties at urban intersection and ramp on urban viaduct at 5.9 GHz

As a hotspot of wireless communication, vehicular communication is playing an important role in the smart city. This study focuses on vehicle-to-vehicle (V2V) radio channel characteristics at 5.9 GHz band based on measurement, under a ramp with soundproof wall on the urban viaduct and an urban intersection scenario, which are two similar but with slight difference propagation environments. Differences of V2V radio channel characteristics between two scenarios have been measured and analysed, in the view of best fit distribution of fades, power delay profile, delay spread, channel gain and Doppler spread. It is found that Weibull and Ricean distribution has a good match in non-line-of-sight and line-of-sight region, respectively. Transformation of different propagation mechanisms can increase or reduce the received power by 9-11 dB on average. Also, the power delay profile and root mean square delay spread are influenced by the different propagation conditions. Moreover, Ricean K-factors and Weibull shape parameters are modelled based on the least-square. The comparison of channel properties between these two classical urban scenarios is vital to the optimal design and performance of V2V communication system.

Millimeter wave wireless interconnects in deep submicron chips: Challenges and opportunities

On-chip wireless links offer the most promising solution to improve performance over traditional Networks-on-Chip (NoCs). Though, significant advancements are being made to support intra-chip wireless communication, a complete understanding of on-chip wireless channel, that facilitates design optimization of transceivers and antennas is still lacking. In this work, we derive on-chip wireless channel characteristics, taking into account antenna implementation, near field and multipath propagation effects. These observations are then used to study impact on wireless NoC performance, packet energy, delay and bandwidth. The study provides crucial insights for circuit designers to tune transceiver and antenna specifications to achieve desired network performance.

Wireless Channel Modeling Simulation and Hardware Implementation

Channel simulator is an important part of the accurate evaluation of the fading characteristics of wireless channel. Efficient design and implementation of wireless channel simulator is very important for the design and verification of wireless systems. The greatest impact on the wireless communication system is a small-scale fading variation. According to the transmission characteristics, this paper analyzed the small scale fading model, the mathematical modeling simulation and hardware implementation. The measured results show that the statistical characteristics of hardware simulators output decline signal in conformity with the theoretical value, can simulate the attenuation, decline of wireless communication system, and doppler frequency shift and other transmission characteristics.

A novel 3D ray launching technique for radio propagation prediction in indoor environments.

Radio propagation prediction simulation methods based on deterministic technique such as ray launching is extensively used to accomplish radio channel characterization. However, the superiority of the simulation depends on the number of rays launched and received. This paper presented the indoor three-dimensional (3D) Minimum Ray Launching Maximum Accuracy (MRLMA) technique, which is applicable for an efficient indoor radio wave propagation prediction. Utilizing the novel MRLMA technique in the simulation environment for ray lunching and tracing can drastically reduce the number of rays that need to be traced, and improve the efficiency of ray tracing. Implementation and justification of MRLMA presented in the paper. An indoor office 3D layouts are selected and simulations have been performed using the MRLMA and other reference techniques. Results showed that the indoor 3D MRLMA model is appropriate for wireless communications network systems design and optimization process with respect to efficiency, coverage, number of rays launching, number of rays received by the mobile station, and simulation time.

Narrowband Characterization of Near-Ground Radio Channel for Wireless Sensors Networks at 5G-IoT Bands.

In this contribution, a narrowband radio channel model is proposed for rural scenarios in which the radio link operates under near-ground conditions for application in wireless sensor networks dedicated to smart agriculture. The received power attenuation was measured for both transmitter and receiver antennas placed at two different heights above ground: 0.2 and 0.4 m. Three frequency ranges, proposed for future 5G-IoT use case in agriculture, were chosen: 868 MHz, 2.4 GHz and 5.8 GHz. Three ground coverings were tested in a rural scenario: soil, short and tall grass fields. The path loss was then estimated as dependent of the radio link range and a three-slope log-normal path loss model was tailored. Results are explained in terms of the first Fresnel zone obstruction. Commercial Zigbee sensor nodes operating at 2.4 GHz were used in a second experiment to estimate the link quality from the experimental Radio Signal Strength Indicator (RSSI) received values. Two sensor nodes were placed at the same elevation above ground as in the previous experiment, only for short grass field case. The Quality of Service performance was determined in terms of theoretical bit error rate achieved for different digital modulations—BPSK, 8PSK and 16QAM—concluding remarkable results for an obstructed radio link.

Deterministic Propagation Modeling for Intelligent Vehicle Communication in Smart Cities.

Vehicular Ad Hoc Networks (VANETs) are envisaged to be a critical building block of Smart Cities and Intelligent Transportation System (ITS) where applications for pollution, congestion reduction, vehicle mobility improvement, accident prevention and safer roads are some of the VANETs expected benefits towards Intelligent Vehicle Communications. Although there is a significant research effort in Vehicle-to-Infrastructure (V2I) and Vehicle-to-Vehicle (V2V) communication radio channel characterization, the use of a deterministic approach as a complement of theoretical and empirical models is required to understand more accurately the propagation phenomena in urban environments. In this work, a deterministic computational tool based on an in-house 3D Ray-Launching algorithm is used to represent and analyze large-scale and small-scale urban radio propagation phenomena, including vehicle movement effects on each of the multipath components. In addition, network parameters such as throughput, packet loss and jitter, have been obtained by means of a set of experimental measurements for different V2I and V2V links. Results show the impact of factors such as distance, frequency, location of antenna transmitters (TX), obstacles and vehicle speed. These results are useful for radio-planning Wireless Sensor Networks (WSNs) designers and deployment of urban Road Side Units (RSUs).

Spatial signature for secure MISO‐OFDM systems

Physical layer security is a promising approach to establish secure communications based on the characteristics of wireless channels. A spatial signature based secure multiple-input single-output (MISO) orthogonal frequency division multiplexing (OFDM) system is proposed to disrupt the reception of a passive eavesdropper by holding two practically relevant assumptions: a limited feedback link for legitimate node and the unavailability of channel state information of eavesdropper. The proposed algorithm achieves a higher average secrecy rate than the conventional secure MISO-OFDM systems in presence of a limited feedback link.

Improving RSSI-Based Path-Loss Models Accuracy for Critical Infrastructures: A Smart Grid Substation Case-Study

IoT is rapidly expanding to all productive sectors; however, as thousands of devices are envisioned to be deployed, a careful study of the radio spectrum (and its interferences) must be considered to predict and improve the network performance. In this sense, radio-channel characterization is essential; in particular, path-loss characterization allows to mathematically predict the propagation behavior and interferences of IoT devices with precision. In this paper, we show that by means of a set of mathematical corrections and measuring procedures, we can soundly employ the received signal strength indicator (RSSI), available in most IoT motes, to derive accurate path-loss models of industrial infrastructures. Experimental results reveal that the proposed scheme substantially improves the characterization accuracy of a real smart grid environment. This, in turn, is proven to have a measurable positive impact on the planning stage of an IoT network, whose life-of-time and cost analysis can be better anticipated.

Wireless channel parameter estimation algorithms: Recent advances and future challenges

Temporal and three-dimensional (3D) spatial information is important for the characterization of wireless channels. In this paper, the commonly used array signal processing (ASP) methods to estimate channel parameters are summarized. Firstly, algorithms that can be used to estimate azimuth angle of arrival (AAoA) and elevation AoA (EAoA) are introduced. They include multiple signal classification (MUSIC), estimation of signal parameter via rotational invariance techniques (ESPRIT), and Unitary ESPRIT algorithms. Secondly, algorithms that can be used to jointly estimate delay, AAoA, and EAoA are given. They include joint angle and delay estimation (JADE) MUSIC, JADE ESPRIT, shift-invariance (SI) JADE, and space-alternating generalized expectation-maximization (SAGE) algorithms. We also propose an improved SI-JADE algorithm to further reduce computation complexity by incorporating with the Unitary ESPRIT algorithm. Performance of the above algorithms to extract only spatial information and to jointly extract temporal and spatial information is compared in both synthetic and 60 GHz real channel environments. Simulation results show that with the inclusion of delay estimation, the joint temporal and spatial estimation algorithms can provide better resolution than algorithms estimating only angles. Measurement data processing results show that MUSIC algorithm can provide comparable results with SAGE algorithm in estimating AAoA and EAoA. SI-JADE and the improved SI-JADE algorithms are also applicable to process 60 GHz channel measurement data. However, MUSIC, SI-JADE, and the improved SI-JADE algorithms can greatly reduce computational burden compared with SAGE algorithm. At last, some future directions are pointed out.

Indoor dual polarised radio channel characterisation in the 54 and 70 GHz bands

In this study, results of wideband dual polarised measurements conducted in indoor environments including office, factory, corridor and computer foyer, using state-of-the-art 2×2 multiple-input–multiple-output frequency modulated continuous wave-based channel sounder, are presented. The measurements were performed in two frequency bands with 6 GHz bandwidth, centred at 54 and 70 GHz, with directional steerable ∼20 dBi (18° beamwidth) horn antennas. Using twists at the transmitter and at the receiver simultaneous co-polar and cross-polar measurements were performed to quantify the polarisation effects on channel parameters such as angular spread, delay spread and path loss. The results show that the co-polarised radio links experienced lower angular spread and delay spread compared with the cross-polarised links. For co-polarised links, the estimated synthesised omnidirectional path loss exponent was found to be in the range of 1.5–2 (close-in model) and 0.9–1.9 (log-distance model) in the respective environments. In individual scenarios, the median cross-polarisation ratio was found to be within 11.7–14.4 and 7.5–17.6 dB at 54 and 70 GHz, respectively.

5.9 GHz vehicular channels comparisons between two traffic status for dense urban area

This study focused on differences in vehicle-to-vehicle radio channel characteristics in the same region but different traffic density and speeds at 5.9 GHz (congestion and non-congestion). The continuous measurement campaign was conducted on a city expressway through the complex dense urban area in Wuhan, China. Small-scale channel characteristics including power delay profile, amplitude fading distribution, K-factor, delay spread and Doppler shift were obtained, respectively. Specifically, the cumulative distribution function of root mean square delay spreads and root mean square Doppler spreads in the non-congested scenario and congested scenario were all fitted well with Lognormal distribution. We also found out that different intensity of traffic and speed of vehicles have little effect on root mean square delay spreads, but have a big impact on root mean square Doppler spreads and level crossing rate. According to estimation outcomes, the V2V channel characteristics for urban areas in Chinese big city were different from the previous measured results under similar scenarios in Europe. Delay spread and level crossing rate in this study can provide significant references to design the wireless communication system for vehicle-to-vehicle channel.